Kinetic studies to determine the proliferative pattern of leukemic cells from the bone marrow of patients with acute leukemia before, during and after cytostatic therapy could add to a rational selection of drugs and drug treatment schemes. The in vivo effects and time course of effects on the cell cycle of leukemic cells of some drugs singly and in combination have been determined. We propose to use the knowledge gained in the past from these drug studies to evaluate drug combinations. We also propose to evaluate some drugs singly, especially investigational drugs. The studies will be done in patients with acute leukemia who are difficult to treat--that is, patients with AML; patients with ALL who have poor risk factors (T lymphoblasts plus other signs to suggest poor risk); and patients with any form of acute leukemia at time of relapse. The following studies will be done on bone marrow samples before and after giving drug or drug combination: (1) bone marrow biopsy and aspirate; (2) labelling index (autoradiograph using HT3), mitotic index and buffy coat; (3) scintillation counts (uptake of HT3 per 1 times 10 to the 6th power); (4) viability; (5) profile of DNA content of cells in cell cycle (as demonstrated by Cytofluorograf); (6) cell size (as determined by cytograph); (7) cellular deoxyribonucleotide pools assay; and (8) in patients with AML only, agar culture of the bone marrow using the Dicke method as described recently.